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Flexible bond wire capacitive strain sensor for a vehicle tyre

Cao, Siyang (2016)
Ph.D. thesis, University of Birmingham.

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Abstract

This thesis reports a novel flexible wire bond structured capacitive sensor design that can measure the strain in the tyres stably and reliably without any influence or disturbance to the tyre material during the measurement. An industry achievable fabrication method based on the design has been also investigated and it is also believed that there is a possibility of introducing the sensor into mass production.

Bond wire technology, laser machining technology and photolithography technology are adopted to fabricate the strain sensor, in which the wire bonding technology is the most significant process for this design. An array of 25 micrometer bond wires that are normally employed for electrical connections in integrated circuits is built to create an interdigitated structure and generating approximately 10pF capacitance. The array that in an approximately 8*8 mm area consists of 50 wire loops and creates 49 capacitor pairs. The aluminium wires are bonded to a flexible PCB which is specially finished to allow direct bonding to copper surface. The wire array is finally packaged and embedded in a flexible and compliant material, polydimethylsiloxane (PDMS), which acts as the structural material that is strained. The implementations of the bond wire, the flexible PCB and PDMS embedding minimize the stiffness of the strain sensor while the PDMS can also prevent the sensor from any potential damage. When a tensile strain occurs, the wires are stretched further apart reducing the capacitance. On the contrary, the wires move closer and increase the capacitance if the strain sensor is compressed. Different from the traditional interdigital capacitor, the capacitance of the device is almost in a linear relationship with respect to the strain, which can measure the strain up to at least ±60000 micro-strain (±6%) with the resolution of 111 micro-strain (0.01%).

Type of Work:Ph.D. thesis.
Supervisor(s):Anthony, Carl and Olatunbosun, O. A.
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Mechanical Engineering
Subjects:TJ Mechanical engineering and machinery
TL Motor vehicles. Aeronautics. Astronautics
Institution:University of Birmingham
ID Code:6619
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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